Organic electroluminescence devices (organic EL devices) are a generic term of devices using organic compounds as a light emission material of a light emission layer and a charge transport material. In manufacture of organic EL devices, a method in which a solution of a polymer materials is wet-coated is excellent in productivity to a method in which a low molecule is vapor-deposited.
However, when a laminate structure is fabricated by wet-coating, there is a problem that a layer coated earlier dissolves in a solvent contained in a layer coated later and a laminate structure cannot be fabricated. Therefore, methods in which a layer is made solvent-insoluble by crosslinking the layer are proposed.
One of the methods involves that a crosslinking group is synthetically bonded to a polymer compound itself having light emissiveness and charge transportability (see Patent Documents 1 to 3). However, as in these prior art documents, a synthetic process is complicate to synthetically bond a crosslinking group to a polymer compound itself having light emissiveness and charge transportability.
Patent Documents 4 and 5 involve that a low molecular compound having light emissiveness and charge transportability is mixed with a polymer compound having a crosslinking group, and that a polymer compound having light emissiveness and charge transportability is mixed with a polymer compound having a crosslinking group or a low molecular compound having a crosslinking group represented by an aromatic bis-azide, as a crosslinking agent. However, if a crosslinking agent having a crosslinking group has an aromatic ring, the light emissiveness and charge transportability which a light emission material and a charge transport material have by nature may be adversely affected.
As methods other than crosslinking, there is a method in which solutions of different polarities are used for adjacent layers. For example, a method is commonly used in polymer organic EL, in which method a water-soluble PEDOT:PSS is used for a hole injection layer so that the layer does not dissolve even if an oil-soluble light emission layer is applied for an upper layer. However, obtained devices do not have a sufficient performance.
Patent Document 6 discloses an organic EL device provided with a first organic layer and a second organic layer, characterized in that the first organic layer contains a polymer having carrier transportability and light emissiveness and a low molecular crosslinking agent having functional groups, and the low molecular crosslinking agent is crosslinked in the first organic layer. However, the low molecular crosslinking agent having two to four functional groups is used and the method has problems in curability of the organic layer and easiness of fabrication of the layer structure.    Patent Document 1: U.S. Pat. No. 6,107,452    Patent Document 2: US2002/106529 (JP-A-2002-170667)    Patent Document 3: WO96/20253 (JP-A-10-511718)    Patent Document 4: WO2002/10129 (JP-A-2004-505169)    Patent Document 5: WO2004/100282    Patent Document 6: US2005/0186106A1